Three-stage evaporation of Cu(In,Ga)S2 solar cell absorber films without KCN treatment and Na control

Cu-poor Cu(In,Ga)S2 films have been prepared by three-stage sequential evaporation ((In,Ga)-S/Cu-S/(In,Ga)-S) on Mo covered soda-lime glass without Na control. The depth profiles of O and Na in the grown films were investigated by secondary ion mass spectroscopy (SIMS). It has been found that the O-concentration was constant in the bulk, and decreased close to the surface comparable to the case of the two-stage process. The observed depth profile of Na resembles that of O. The efficiencies of solar cells from the O2-annealed Cu-rich Cu(In,Ga)S2 films did not increase, but the efficiencies of some solar cells prepared from Cu-poor Cu(In,Ga)S2 films increased when the absorber was annealed in oxygen. The best efficiency of a solar cell from our O2-annealed Cu-poor Cu(In,Ga)S2 films was 9.3% (no antireflection coating) without KCN treatment and Na control.